1 The people who succumb to this quiet killer often are stronger swimmers than the lifeguards on duty. Therefore, lifeguards tend not to worry about them or watch them carefully.

2 Breath-holding activities occur underwater, and the natural ripples on the surface can obscure an individual’s presence on the bottom of the swimming pool.

3 Reflection and refraction produced by the surface “ripple effect” often make the motionless bodies on the bottom of the pool appear to be moving, so the lifeguards, parents or supervisors do not detect distress.

4 When a good swimmer is detected on the bottom, denial and delay often lead to unsuccessful recoveries.